1. Field of the Invention
The present invention relates generally to a storage medium and storage medium recording method for functionally expanding a magneto-optical disc usable by a conventional mini-disc (MD) system, the expansion being made in such a manner as to maintain compatibility with the conventional MD system.
2. Discussion of the Background
The so-called Mini-disc (MD), a 64 mm-across magneto-optical disc housed in a cartridge, has gained widespread acceptance today as a storage medium to and from which digital audio data are recorded and reproduced.
The MD system adopts ATRAC (Adaptive TRansform Acoustic Coding) as its audio data compression method. ATRAC involves compression-coding audio data by what is called MDCT (Modified Discrete Cosine Transform). The audio data has been acquired through a predetermined time window. Typically, music data are compressed by ATRAC to one-fifth to one-tenth the original size.
The MD system utilizes a convolution code called ACIRC (Advanced Cross Interleave Reed-Solomon Code) as its error correction system and EFM (Eight-to-Fourteen Modulation) as its modulation technique. ACIRC is a convolution code that provides dual error correction on C1 and C2 sequences (in vertical and oblique directions). The method is used to carry out a powerful error correction process on sequential data such as audio data. One disadvantage of ACIRC is that it requires a linking sector arrangement for data update purposes. ACIRC and EFM are basically the same as those employed in a conventional compact disc (CD) system.
For music data management, the MD system uses U-TOC (User TOC [Table of Contents]). Specifically, a U-TOC area is furnished on an inner side of a recordable area of the disc. For the current MD system, U-TOC constitutes the track (audio track/data track) title sequence and management information that is updated to keep up with the recording or deletion of such tracks. Under the U-TOC scheme, each track (i.e., parts constituting each track) is managed in terms of start position, end position, and mode settings.
The disc for the MD system is small, inexpensive, and offers good characteristics when used by the system to record or reproduce audio data. These advantages have enabled the MD system to gain widespread market acceptance.
As recognized by the present inventors, MD systems have not fully achieved their potential in the market as they are not compatible with general purpose computers, such as personal computers. Moreover, convention MD systems use different file management schemes than the File Allocation Table (FAT)-based file systems used in personal computers.
With more general use of personal computers and PC-based networking, more and more audio data are distributed over PC-based networks. Today, it is common practice for the user of a personal computer to use it as an audio server from which to download favorite music files to a portable data reproducing apparatus for music reproduction. As recognized by the present inventors, because the conventional MD system is not fully compatible with personal computers, a new MD system is desirable that would adopt a general-purpose management system, such as a FAT (File Allocation Table) system, to enhance PC-compatibility.
As explained in White, R., “How Computers Work, Millennium Edition” Que Corporation, pages 146 and 158 for example, 1999, the entire contents of which being incorporated herein by reference, the FAT is created by the disk drive on a particular disk sector, such as sector 0. The term “FAT” (or “FAT System”) is used generically herein to describe various PC-based file systems, and is intended to cover the specific FAT-based file systems used in DOS, VFAT (virtual FAT) used in Windows 95/98, FAT 32 used in Windows 98/ME/2000, as well as NTFS (NT file system; sometimes New Technology File System) which is the file system used by Windows NT operating system, or optionally in Windows 2000 operating system, for storing and retrieving files on read/write disks. NTFS is the Windows NT equivalent of the Windows 95 file allocation table (FAT) and the OS/2 High Performance File System (HPFS).
Meanwhile, a higher degree of compatibility with personal computers means increased risk of unauthorized copying of copyrighted works, which in-turn requires better techniques to protect against unauthorized copying of audio works. One technological way of reinforcing copyright laws involves encrypting the audio works when recorded. It is also desired that music titles and artist names recorded on the disc be managed in a more efficient manner than at present.
The current MD system uses a disc with a storage capacity of about 160 MB, which, as recognized by the present inventors, is not always sufficient for the user's requirement for data storage. It is thus desired that the storage capacity of a new disc be boosted while remaining backwards-compatible with the current MD system.